JP6654925B2 - Electrode for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an electrode for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery.

  Lithium-ion secondary batteries are characterized by higher energy density and electromotive force than lead-acid batteries and nickel-metal hydride batteries, so they are widely used as power sources for various portable devices and notebook computers that require miniaturization and weight reduction. It is used. Such a lithium ion secondary battery generally includes a positive electrode sheet in which a positive electrode active material is applied to a positive electrode current collector and a negative electrode sheet in which a negative electrode active material is applied to a negative electrode current collector. The separator is laminated with a separator and an electrolyte interposed therebetween, and the laminate in which the positive electrode sheet, the separator and the negative electrode sheet are laminated is sealed in a case.

For the purpose of preventing a short circuit between a positive electrode and a negative electrode, a separator made of a porous sheet made of a conventional olefin resin or the like is used.
When charging and discharging of the lithium ion secondary battery are repeated, needle-like crystals (dendrites) of lithium metal are deposited on the negative electrode side. When the dendrite extends, the dendrite penetrates through the separator to reach the positive electrode, which may cause an internal short circuit.

  Patent Literature 1 discloses a polymer solid electrolyte in which a foamed film is impregnated with an electrolyte solution containing a lithium salt for the purpose of preventing an internal short circuit due to dendrite elongation.

JP-A-11-86628

  Since the production of the foamed film used for the polymer solid electrolyte of Patent Document 1 requires special temperature and pressure conditions, the production process is complicated and the foamed film has a predetermined expansion ratio stably. Was difficult to produce. As a result, internal short circuit due to dendrite growth could not be sufficiently prevented. Further, it has been difficult to produce a lithium ion secondary battery having stable ion conductivity.

  The present invention has been made in view of the above circumstances, can be manufactured by a simple method, lithium ion secondary battery electrode in which the deposition of lithium metal is suppressed, a method for manufacturing the electrode, and It is an object to provide a lithium ion secondary battery provided with such an electrode.

The present invention has the following aspects.
[1] An electrode for a lithium ion secondary battery in which a current collector, an electrode active material layer, and an insulating mesoporous layer are arranged in this order.
[2] The lithium ion secondary battery according to [1], wherein the electrode for a lithium ion secondary battery is a negative electrode, and a covalent bond is formed at least at a part of an interface between the electrode active material layer and the mesoporous layer. Electrodes for batteries.
[3] The lithium ion secondary battery according to [1], wherein the electrode for a lithium ion secondary battery is a positive electrode, and a covalent bond is formed at least at a part of an interface between the electrode active material layer and the mesoporous layer. Electrodes.
[4] The electrode for a lithium ion secondary battery according to [2], wherein the electrode active material layer contains silicon or silicon oxide.
[5] The electrode for a lithium ion secondary battery according to [3], wherein the electrode active material layer contains a metal oxide.
[6] A lithium ion secondary battery provided with the electrode for a lithium ion secondary battery according to any one of [1] to [5].
[7] A precursor solution containing an organic-inorganic composite crosslinkable compound having a crosslinkable silyl group and a carbon atom covalently bonded thereto is applied to the surface of the electrode active material layer laminated on the current collector. Forming an insulating mesoporous layer on the surface of the electrode active material layer by hydrolyzing and condensing the crosslinkable silyl group of the organic-inorganic composite crosslinkable compound in the precursor solution. And a method for producing an electrode for a lithium ion secondary battery comprising:
[8] a step of applying a precursor solution containing an organic-inorganic composite crosslinkable compound having a crosslinkable silyl group and a carbon atom covalently bonded thereto to a substrate, and hydrolyzing and condensing the crosslinkable silyl group Forming an insulating mesoporous layer on the substrate, separating the insulating mesoporous layer from the substrate, and applying a primer solution containing a silane coupling agent to one surface of the mesoporous layer. By applying and applying the applied surface to the surface of the electrode active material layer laminated on the current collector, the insulating mesoporous layer is provided on the surface of the electrode active material layer via the silane coupling agent. And a method for producing an electrode for a lithium ion secondary battery, comprising:

In the lithium ion secondary battery using the electrode for a lithium ion secondary battery of the present invention, the adhesion of the insulating mesoporous layer to the electrode active material layer is high, so that the deposition of lithium metal on the surface of the electrode active material layer and Elongation of dendrite can be suppressed, and short circuit between the positive electrode and the negative electrode can be suppressed.
According to the method for producing an electrode for a lithium ion secondary battery of the present invention, the above excellent electrode can be produced by a simple method.

FIG. 1 is a sectional view schematically showing an electrode for a lithium ion secondary battery according to a first embodiment of the present invention. It is a sectional view showing the outline of the lithium ion secondary battery of a first embodiment of the present invention.

  Hereinafter, preferred embodiments of a lithium ion secondary battery electrode of the present invention, a lithium ion secondary battery using the same, and a method for manufacturing a lithium ion secondary battery electrode will be described with reference to the drawings.

<Electrode for lithium ion secondary battery>
The electrode for a lithium ion secondary battery according to the first aspect of the present invention is an electrode in which a current collector, an electrode active material layer, and an insulating mesoporous layer are stacked and arranged in this order.

  In the first embodiment of the electrode for a lithium ion secondary battery (hereinafter, simply referred to as “electrode”) of the present invention, as shown in FIG. 1, an electrode active material layer containing an electrode active material is provided on a current collector 1a. An electrode 1 comprising an electrode active material layer 1b and an insulating mesoporous layer 1c formed on the electrode active material layer 1b. The electrode 1 may be a positive electrode or a negative electrode.

(Current collector 1a and electrode active material layer 1b)
As the current collector 1a and the electrode active material layer 1b used in the present embodiment, conventionally known electrodes can be used. For example, a paste-like composition containing an electrode active material, a conductive auxiliary agent, a binder (binder), a solvent and the like is applied on the current collector 1a and dried to form an electrode active material layer 1b on the current collector 1a. Examples include a formed composite electrode and a sputtered electrode in which an electrode active material layer 1b is formed on the surface of a current collector 1a by a sputtering method.

(Positive electrode)
When the electrode 1 is a positive electrode, an electrode active material layer 1b containing a positive electrode active material is laminated on the surface of the current collector 1a.
As the current collector 1a, for example, a metal foil such as an aluminum foil is used. The thickness of the current collector 1a is preferably 10 μm to 25 μm. The thickness of the electrode active material layer 1b containing the positive electrode active material is preferably 10 μm to 100 μm.

As the positive electrode active material, a metal oxide is used. The metal oxide includes, for example, a lithium metal oxide compound represented by a general formula LiM _x O _y (where M is a metal and x and y are the composition ratios of the metal M and oxygen O). .
Specifically, lithium cobaltate, lithium iron phosphate, lithium nickelate, lithium manganate and the like are used as the lithium metal oxide compound. As other metal oxides, ternary (nickel / manganese / cobalt, nickel / cobalt / aluminum) and the like are used. As the positive electrode active material, a composite product containing at least two of the above-described lithium metal oxide compound and metal oxide can be used.

  Examples of the conductive assistant constituting the positive electrode include carbon materials such as carbon black such as Ketjen black and acetylene black, graphite (graphite), carbon nanotube, carbon nanohorn, graphene, and fullerene.

  When the metal oxide or graphite is contained in the positive electrode active material layer 1b, -OH groups exist on the surface of the positive electrode active material layer 1b. The -OH group of the positive electrode active material layer 1b is useful for improving the adhesiveness to the mesoporous layer 1c. For example, when the material of the mesoporous layer 1c (for example, a silane compound having an alkoxy group) is applied on the positive electrode active material layer 1b to form the mesoporous layer 1c, the -OH group reacts with the alkoxy group. Thus, a covalent bond (Si-OC bond) can be formed. As a result, the positive electrode active material layer 1b and the mesoporous layer 1c are firmly adhered, the structural strength of the electrode 1 is increased, and deterioration due to expansion and contraction due to charge and discharge is suppressed.

(Negative electrode)
When the electrode 1 is a negative electrode, an electrode active material layer 1b containing a negative electrode active material is laminated on the surface of the current collector 1a.
As the current collector 1a, for example, a metal foil such as a copper foil is used. The thickness of the current collector 1a is preferably 10 μm to 25 μm. The thickness of the electrode active material layer 1b containing the negative electrode active material is preferably 10 μm to 100 μm.

Examples of the negative electrode active material include carbon materials such as silicon, silicon oxide, graphite, hard carbon, and soft carbon, and tin. As a suitable negative electrode active material of the present embodiment, for example, silicon oxide is given.
Examples of silicon oxide include those represented by the general formula “SiO _x (where x is any number from 0.5 to 1.5)”. Here, when silicon oxide is viewed in “SiO” units, this SiO is amorphous SiO or around the nanocluster Si so that the molar ratio of Si: SiO ₂ is about 1: 1. Is a composite of Si and SiO _{2 in} which SiO ₂ exists. It is assumed that SiO ₂ has a buffering effect on the expansion and contraction of Si during charge and discharge.

The silicon oxide is preferably in the form of particles. As for the size of the particulate silicon oxide, for example, the average particle diameter is preferably from 0.1 to 30 μm, more preferably from 1 to 20 μm, further preferably from 1 to 10 μm.
When the value is equal to or more than the above lower limit, the negative electrode active material layer 1b tends to be porous, and the permeability of the electrolytic solution is increased. When the thickness is equal to or less than the above upper limit, the structural strength of the negative electrode active material layer 1b increases, and deterioration due to expansion and contraction due to charge and discharge is suppressed.

  As a method of measuring the average particle diameter of silicon oxide, for example, using an electron microscope, measure the particle diameter of about 100 arbitrary silicon oxide particles used for the negative electrode material, calculate the average value and determine Method.

  When silicon oxide is contained in the negative electrode active material layer 1b, a large number of -OH groups derived from silicon oxide exist on the surface of the negative electrode active material layer 1b. The -OH group of the negative electrode active material layer 1b is useful for improving the adhesion to the mesoporous layer 1c. For example, when the material of the mesoporous layer 1c (for example, a silane compound having an alkoxy group) is applied on the negative electrode active material layer 1b to form the mesoporous layer 1c, the -OH group reacts with the alkoxy group. Thus, a covalent bond (Si-OC bond) can be formed. As a result, the negative electrode active material layer 1b and the mesoporous layer 1c are firmly adhered, the structural strength of the electrode 1 is increased, and deterioration due to expansion and contraction due to charge and discharge is suppressed.

In the present embodiment, the electrode active material layer 1b is stacked on one surface of the current collector 1a, but the electrode active material layers 1b may be formed on both surfaces of the current collector 1a.
Of the electrode active material layers 1b formed on both surfaces of the current collector 1a, it is sufficient that the mesoporous layer 1c is formed on at least one surface of the electrode active material layer 1b, and the mesoporous layer 1b is formed on both surfaces of the electrode active material layer 1b. 1c is preferably formed.

(Mesoporous layer 1c)
As shown in FIG. 1, an insulating mesoporous layer 1c is formed on the electrode active material layer 1b of the electrode 1 of the present embodiment.
The mesoporous layer in this specification is a porous layer containing an inorganic substance in which a large number of mesoporous holes (mesopores) are formed. The mesoporous layer 1c preferably has a continuous pore structure in which a large number of mesoporous pores are continuously connected. Here, the continuous pore structure refers to a structure in which holes are continuously connected, but these holes do not necessarily have to be completely continuous in the entire range.

  The pores in the continuous pore structure are bicontinuous. The bicontinuous structure can be mathematically expressed as a gyroid or a double groid (Double Gyroids), and means that the structure itself and the vacancy are connected to each other continuously (Reference: SCIENCE, p 1716, Vol.286, 26 Nov., 1999).

  Generally, the diameter of the opening of a mesoporous hole defined as a technical term is 2 nm to 50 nm. Whether the mesoporous layer 1c of the present embodiment has a continuous pore structure composed of mesoporous pores is determined by a known mercury porosimetry method (mercury intrusion method) with pores (voids) having a diameter of 2 nm to 50 nm. Is performed by confirming whether or not there are a plurality.

  The mesoporous layer 1c is preferably a layer having a crosslinked structure by a metal or silicon-oxygen bond, and having a continuous pore structure in which pores formed by the crosslinked structure are continuously connected. Preferably, the metal is a metal oxide.

  The porosity based on the total volume of the mesoporous layer 1c is preferably 30 to 80%, and more preferably 40 to 70%. When the porosity is 30% or more, ion diffusion is enhanced and the rate characteristics are improved, and when the porosity is 80% or less, the structure becomes strong, and lithium precipitation hardly occurs. The porosity in the present embodiment is calculated by a mercury porosimetry method.

The average pore diameter of the mesoporous layer 1c is preferably 2 nm to 1000 nm, more preferably 5 nm to 500 nm, further preferably 10 nm to 250 nm, and particularly preferably 20 to 50 nm. When the average of the pore diameters is equal to or more than the lower limit of the above range, the electrolyte is easily diffused in the mesoporous layer 1c, and the ion transport rate can be further increased.
If the average pore diameter is equal to or less than the upper limit of the above range, even if lithium metal is deposited on the surface of the electrode active material layer 1b, the dendrite made of lithium metal will pass through the porous structure of the mesoporous layer 1c and extend. Can be easily prevented.
The average diameter of the holes in the present embodiment can be measured by a known mercury porosimetry method.

The thickness of the mesoporous layer 1c is, for example, preferably 1 to 20 μm, and more preferably 3 to 10 μm.
When the thickness of the mesoporous layer is 1 μm or more, the insulating properties between adjacent electrodes can be sufficiently maintained, and the dendrite can be prevented from extending and reaching the adjacent electrodes (short circuit). When the thickness of the mesoporous layer is 20 μm or less, the electrolyte is easily diffused in the mesoporous layer 1c, and the ion transport rate can be further increased.
Here, the thickness of the mesoporous layer 1c is a value represented by an average obtained by measuring the thickness of the mesoporous layer 1c at any five points using a contact-type thickness gauge. When it is difficult to directly apply a contact-type thickness gauge when measuring the thickness of the mesoporous layer, in a state where other layers such as the current collector 1a and the electrode active material layer 1b are stacked, The total thickness may be measured in the same manner as described above, and the difference may be calculated by taking the difference from the thickness of another layer (measured by the same method as described above).

The mesoporous layer 1c preferably includes a structure having a crosslinked structure composed of an organic-inorganic composite crosslinkable compound having a siloxane bond and a carbon atom bonded to silicon in the siloxane bond.
The carbon atom preferably constitutes a divalent linear or branched hydrocarbon group having 1 to 50 carbon atoms. By being a hydrocarbon group, flexibility is imparted and physical properties of the film can be controlled. Examples of the hydrocarbon group include an alkylene group and an aromatic-containing group, and preferably a straight-chain alkylene group.

  As a specific example of the structure, for example, a structure represented by the general formula (1) (hereinafter, referred to as structure 1) is given.

（式中、Ｘは−Ｏ−結合又はＯＨ基であり、Ｒ^１は炭素数１〜５０の炭化水素基であり、Ｒ^２はメチル、エチル、プロピル、又はフェニル基のいずれかの基を表し、ｎ１，ｎ２は０，１，２のいずれかであり、ｎ１，ｎ２の少なくとも一つが１または２である。）

(In the formula, X is an —O— bond or an OH group, R ¹ is a hydrocarbon group having 1 to 50 carbon atoms, and R ² represents a methyl, ethyl, propyl, or phenyl group. , N1 and n2 are any of 0, 1 and 2, and at least one of n1 and n2 is 1 or 2.)

X in the formula (1) can form a bridge between the structures (1).
When the carbon number of R ¹ is 50 or less, dense crosslinking is easily formed. When R ¹ has 1 or more carbon atoms, mesoporous pores are easily formed. In addition, when R ¹ is a hydrocarbon group, deterioration due to acid or heat is less likely to occur as compared with the case where R ¹ has some hetero atom (atom other than carbon and hydrogen).

The hydrocarbon group is preferably a group represented by the following formula (2).
N in the following formula (2) is preferably 1 to 20, and more preferably 8 to 12. Thereby, heat resistance and flexibility are improved.
Since the linear polymethylene chain has a bendable structure, the mesoporous layer can be given an appropriate degree of flexibility, and the density and the like can be adjusted. These adjustments are performed mainly by adjusting the molecular length of the polymethylene chain.

A structure (3) comprising an organic-inorganic composite crosslinkable compound represented by the following formula (3), wherein R ¹ in the formula (1) is an n-octylene group and R ² is a methyl group, is desirable. Since this structure (3) has a group in which methylene is linked in eight chains (linear octylene group), the balance between crosslinkability, flexibility and heat resistance is improved.

（ 式中、Ｘは−Ｏ−結合又はＯＨ基であり、ｎ１，ｎ２は０，１，２のいずれかであり、ｎ１，ｎ２の少なくとも一つが１または２である。）

(In the formula, X is an —O— bond or an OH group, n1 and n2 are either 0, 1, or 2, and at least one of n1 and n2 is 1 or 2.)

The structure may have a structure in which a plurality of types of structural units are bonded to each other. For example, a structure in which the organic-inorganic composite unit of n1 = 1 and the organic-inorganic composite unit of n2 = 2 in the general formula (1) may be combined. In this case, the crosslink density and the like can be adjusted, and as a result, the void structure, flexibility (flexibility), and the like of the mesoporous layer can be adjusted.
In addition, the physical properties of the mesoporous layer can be adjusted by including the above-mentioned structure in which organic-inorganic composite units having different organic chain lengths and different types of substituents are bonded.

(About the interface between the electrode active material layer 1b and the mesoporous layer 1c)
When the electrode 1 is a negative electrode, it is preferable that a covalent bond is formed at least at a part of the interface between the electrode active material layer 1b and the mesoporous layer 1c.
For example, when the mesoporous layer 1c containing a siloxane component is formed on the negative electrode active material layer 1b containing silicon oxide (SiOx), at least a portion of the siloxane component contained in the mesoporous layer 1c is It is preferably covalently bonded to SiOx as an active material.
Whether or not the covalent bond is formed depends on the method of forming the mesoporous layer 1c. For example, when the precursor of the siloxane component, which is the raw material of the mesoporous layer 1c, undergoes a polymerization reaction on the surface of the negative electrode active material layer 1b containing SiOx to form the mesoporous layer 1c, a covalent bond is formed at the interface. Is done. The covalent bond is also formed when the mesoporous layer 1c is bonded to the surface of the negative electrode active material layer 1b containing SiOx via a silane coupling agent.

<Lithium ion secondary battery>
A lithium ion secondary battery according to a second aspect of the present invention includes the electrode for a lithium ion secondary battery according to the first aspect as a positive electrode or a negative electrode.
FIG. 2 is a diagram showing an example of the lithium ion secondary battery according to the present invention. The lithium ion secondary battery 10 in FIG. 2 includes a current collector 11a, a negative electrode 11 having a negative electrode active material layer 11b and a mesoporous layer 1c, an electrolyte (electrolyte layer) 2, a current collector 12a and a positive electrode active material layer 12b. And a positive electrode 12.

The negative electrode 11 is the electrode according to the first aspect of the present invention. The configuration of the positive electrode 12 is the same as that of a known positive electrode of a lithium ion secondary battery.
The electrolyte 2 is not particularly limited, and for example, a known electrolyte, an electrolyte, and the like used in a known lithium ion secondary battery can be applied. Examples of the electrolyte include a mixed solution in which an electrolyte salt is dissolved in an organic solvent. As the organic solvent, those having resistance to high voltage are preferable, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, Examples thereof include polar solvents such as 1,2-diethoxyethane, tetrohydrafuran, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, and a mixture of two or more of these solvents. As the electrolyte salt, for example, in the case of a lithium ion secondary battery, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₆ , LiCF ₃ CO ₂ , LiPF ₆ SO ₃ , LiN (SO ₃ CF ₃ ) ₂ , Li ( A salt containing lithium such as SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂ CF ₃ ) ₂ , or a mixture of two or more of these salts is given.

  In the lithium ion secondary battery 10 of FIG. 2, the mesoporous layer 1c is formed on the surface of the negative electrode active material layer 11b, but the present invention is not limited to this, and the mesoporous layer is formed on the surface of the positive electrode active material layer 12b. It can be done.

  In the lithium ion secondary battery 10 of FIG. 2, since the mesoporous layer 1c can serve as a separator, no separator is provided. However, the present invention is not limited to this. Good. The separator is disposed between the negative electrode 11 and the positive electrode 12. The material of the separator is not particularly limited. For example, a material made of olefin-based polyethylene, polypropylene, or cellulose-based material can be used. A nonwoven fabric or the like made of these materials can be used as the separator.

<Method for producing electrode for lithium ion secondary battery>
A third aspect of the present invention is a method for producing an electrode for a lithium ion secondary battery according to the first aspect. Hereinafter, two embodiments will be described.

(First embodiment)
The production method of the first embodiment is to prepare a precursor solution containing a crosslinkable silyl group and an organic-inorganic composite crosslinkable compound having a carbon atom covalently bonded to the crosslinkable silyl group. A step of applying to the surface of the electrode active material layer laminated thereon; and hydrolyzing and condensing the crosslinkable silyl group of the organic-inorganic composite crosslinkable compound in the precursor solution, thereby forming the electrode active material. Forming an insulating mesoporous layer on the surface of the material layer.

  The crosslinkable silyl group forms a crosslinked structure composed of a siloxane bond (—Si—O—Si—) by hydrolysis and subsequent dehydration condensation reaction. Examples of the crosslinkable silyl group include an alkoxysilyl group in which an alkoxy group such as methoxy, ethoxy, propoxy, and phenoxy is directly bonded to a silicon atom, a halogenated silyl group in which a halogen such as chlorine is bonded to a silicon atom, and an acetoxy group. And the like.

  The carbon atom preferably constitutes a divalent linear or branched hydrocarbon group having 1 to 50 carbon atoms. Examples of the hydrocarbon group include an alkylene group and an aromatic-containing group, and preferably a straight-chain alkylene group.

  The organic-inorganic composite crosslinkable compound preferably has two or more crosslinkable silyl groups, and more preferably has two crosslinkable silyl groups at the terminal of the compound. When a single compound has two or more crosslinkable silyl groups, the individual crosslinkable silyl groups may be the same or different, but from the viewpoint of easy control of the crosslinking reaction, Preferably they are the same. The organic-inorganic composite crosslinkable compound preferably has a molecular weight of 100 to 500.

  Specific examples of the organic-inorganic composite crosslinkable compound include, for example, a compound represented by the general formula (4) (hereinafter, referred to as compound (4)).

（式中、Ｒ^１は炭素数１〜５０の炭化水素基であり、Ｒ^２はメチル、エチル、プロピル、又はフェニル基のいずれかの基を表し、Ｒ^５はＣｌ、ＯＣＨ_３、ＯＣ_２Ｈ_５、ＯＣ_６Ｈ_５、ＯＨ、又はＯＣＯＣＨ_３基のいずれかの基を表し、ｎ１，ｎ２は０，１，２のいずれかであり、ｎ１，ｎ２の少なくとも一つが１または２である。）

(Wherein, R ¹ represents a hydrocarbon group having 1 to 50 carbon atoms, R ² represents a methyl, ethyl, propyl, or phenyl group, and R ⁵ represents Cl, OCH ₃ , OC ₂ H ₅ , OC ₆ H ₅ , OH, or OCOCH ₃ , wherein n 1 and n 2 are 0, 1, 2 and at least one of n 1 and n 2 is 1 or 2.

R ⁵ in the formula (4) can form a bridge between the compounds (4).
When the carbon number of R ⁵ is 50 or less, dense crosslinking can be easily formed. The number of carbon atoms in R ⁵ can be easily formed is the mesoporous pores with one or more. In addition, when R ⁵ is a hydrocarbon group, deterioration due to acid or heat is less likely to occur as compared with the case where R ⁵ has some hetero atom (atom other than carbon and hydrogen).

The hydrocarbon group is preferably a group represented by the following formula (5). N in the following formula (5) is preferably 1 to 20, and more preferably 8 to 12. Thereby, heat resistance and flexibility are improved.
Since the linear polymethylene chain has a bendable structure, the mesoporous layer can be given an appropriate degree of flexibility, and the density and the like can be adjusted. These adjustments are performed mainly by adjusting the molecular length of the polymethylene chain.

A compound represented by the following formula (6) wherein R ¹ in the above formula (4) is an n-octylene group and R ² is a methyl group (hereinafter, compound (6)) is desirable.

（ 式中、Ｘは−Ｏ−結合又はＯＨ基であり、ｎ１，ｎ２は０，１，２のいずれかであり、ｎ１，ｎ２の少なくとも一つが１または２である。）

(In the formula, X is an —O— bond or an OH group, n1 and n2 are either 0, 1, or 2, and at least one of n1 and n2 is 1 or 2.)

The precursor solution may include a plurality of types of organic-inorganic composite crosslinkable compounds. For example, the precursor solution may include an organic-inorganic composite crosslinkable compound with n1 = 1 and an organic-inorganic composite crosslinkable compound with n2 = 2. In this case, the crosslink density and the like can be adjusted, and as a result, the void structure, flexibility (flexibility), and the like of the mesoporous layer can be adjusted.
The physical properties of the mesoporous layer can also be adjusted by using a precursor solution containing a plurality of types of the organic-inorganic composite crosslinkable compounds having different numbers of carbon atoms and types of substituents of R ¹ and R ⁵ .

The solvent constituting the precursor solution may be any solvent that can dissolve or disperse the organic-inorganic composite crosslinkable compound, and is preferably a nonpolar organic solvent such as toluene.
The kind of the organic-inorganic composite crosslinkable compound contained in the precursor solution may be one kind or two or more kinds, but they are different from each other from the viewpoint of easily forming a continuous pore structure. It is preferable that two or more kinds have a crosslinkable silyl group.
The concentration of the organic-inorganic composite crosslinkable compound contained in the precursor solution is preferably, for example, 1 wt% to 50 wt%.

The precursor solution preferably contains a known catalyst that can promote the hydrolysis and condensation of the crosslinkable silyl group. The type of the catalyst is appropriately selected in consideration of the type of the crosslinkable silyl group and the desired reactivity.
If the temperature at the time of adding the catalyst to the precursor solution is lowered, it is possible to prevent the reaction from being excessively accelerated before coating. The temperature is appropriately set between the freezing point and the boiling point of the solvent, and for example, 0 to 40 ° C. is appropriate. The addition of the catalyst to the precursor solution may be performed while cooling.

  The electrode active material layer to which the precursor solution is applied is preferably formed in advance on a current collector. As a coating method, for example, a known solution coating method such as a spin coating method, a dipping method, a printing method, a doctor blade method or the like can be applied.

After applying the precursor solution onto the electrode active material layer, it is preferable to secure a time for the hydrolysis and condensation reactions to proceed, and to cure (stand still).
The temperature at the time of curing is, for example, 5 ° C. to the boiling point, preferably 10 to 40 ° C., in consideration of the boiling point of the solvent.
When the temperature is equal to or higher than the lower limit of the above temperature range, the reaction proceeds sufficiently quickly, and a continuous pore structure can be easily formed.
When the temperature is equal to or lower than the upper limit of the temperature range, it is possible to prevent the reaction from proceeding excessively fast and hindering the formation of the continuous pore structure.
When the reaction is completed, a target electrode having a mesoporous layer formed on the surface of the electrode active material layer is obtained.
In the above reaction, a known covalent bond (for example, a siloxane bond: -Si-O-Si-) is formed at the interface between the mesoporous layer and the electrode active material layer.

After curing, heating may be performed at a temperature higher than the curing temperature to completely remove the solvent and fix the cross-linked structure formed inside the mesoporous layer. The heating temperature is, for example, preferably equal to or higher than the boiling point of the solvent and equal to or lower than 300 ° C, and more preferably 100 to 200 ° C.
When the temperature is equal to or higher than the lower limit of the above temperature range, the solvent can be easily removed.
When the temperature is equal to or lower than the upper limit of the temperature range, deterioration of the electrode due to heat can be prevented.

(Second embodiment)
In the production method of the second embodiment, a precursor solution containing an organic-inorganic composite crosslinkable compound having a crosslinkable silyl group and a carbon atom covalently bonded thereto is prepared, and the precursor solution is applied on a substrate. A step of forming an insulating mesoporous layer on the substrate by hydrolyzing and condensing the crosslinkable silyl group; a step of separating the insulating mesoporous layer from the substrate; A primer solution containing a ring agent is applied to one surface of the mesoporous layer, and the applied surface is brought into contact with the surface of the electrode active material layer laminated on the current collector, so that the surface of the electrode active material layer is Adhering the insulating mesoporous layer via the silane coupling agent.

Since the precursor solution is the same as the precursor solution of the first embodiment, the description is omitted.
The substrate is not particularly limited as long as the precursor solution can be applied, and the applied precursor solution reacts and can support the precursor solution until a mesoporous layer is formed. Examples thereof include those having a flat surface such as a resin film, a glass plate, and a metal plate.

As a method of applying the precursor solution to the surface of the base, the same method as the method of applying the precursor solution to the surface of the electrode active material layer in the first embodiment can be used.
By curing and drying and solidifying the applied precursor solution in the same manner as described above, a target mesoporous layer can be formed on the substrate.

  The method for separating the mesoporous layer from the surface of the substrate is not particularly limited, and the method for peeling (peeling) the mesoporous layer, the method for dissolving the substrate, and the method for immersing the mesoporous layer in a solvent that is difficult to dissolve, A method in which the substrate is dissolved to leave a mesoporous layer.

Known products can be applied to the primer solution and the silane coupling agent.
As a method of applying the primer solution to one surface of the mesoporous layer, a method similar to the method of applying the precursor solution to the surface of the electrode active material layer in the first embodiment is preferable.

The contact surface of the primer solution and the surface of the electrode active material layer previously laminated on the current collector contact the surface of the electrode active material layer with the insulating property via the silane coupling agent. A mesoporous layer can be bonded. A known covalent bond (for example, a siloxane bond: -Si-O-Si-) is formed in a chemical reaction associated with the adhesion.
Through the above steps, a target electrode having the mesoporous layer formed on the surface of the electrode active material layer is obtained.

  As a modified example of the above embodiment, instead of applying the primer solution to the mesoporous layer, the primer solution is applied to the surface of the electrode active material layer, and the mesoporous layer is brought into contact with the applied surface to form the electrode solution. A method of bonding the mesoporous layer to the surface of the active material layer via the silane coupling agent may also be used.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

(Example 1)
(Preparation of precursor containing organic-inorganic composite crosslinkable compound)
First, a method for preparing a precursor containing an organic-inorganic composite crosslinkable compound will be described.
(Synthesis of bifunctional precursor)
In a toluene solution of 11.0 g of 1,7-octadiene (manufactured by Wako Pure Chemical) and 26.9 g of diethoxymethylsilane (manufactured by Shin-Etsu Silicon Co., Ltd.), chloroplatinic acid (manufactured by Wako Pure Chemical) and divinyltetramethyldisiloxane ( A solution of 0.05 mmol of a Karstedt's catalyst (Karsted: USP3775452) prepared from Gelest Co., Ltd.) was mixed and stirred under a nitrogen atmosphere at 30 ° C. for one day. The reaction mixture thus obtained was purified by distillation to obtain 1,8-bis (diethoxymethylsilyl) octane. The structure was confirmed by ¹ H-NMR (nuclear magnetic resonance spectrometer DRX-300 manufactured by Bruker).

(Synthesis of monofunctional precursor)
1,8-bis (dimethylethoxysilyl) octane was obtained in the same manner as in the synthesis of the bifunctional precursor except that dimethylethoxysilane was used in place of diethoxymethylsilane. The structure was confirmed by ¹ H-NMR (nuclear magnetic resonance spectrometer DRX-300 manufactured by Bruker).

0.6 g of 1,8-bis (diethoxymethylsilyl) octane which is a bifunctional precursor obtained by the above-described process, and 0.5 g of 1,8-bis (dimethylethoxylyl) octane which is a monofunctional precursor Was dissolved in 0.8 g of isopropanol to form an isopropanol solution.
Further, 0.2 g of 7N hydrochloric acid was added to 0.8 g of isopropanol. This solution and the isopropanol solution containing the aforementioned bifunctional precursor and monofunctional precursor were combined and stirred for several tens of seconds to form a precursor solution.

(Formation of mesoporous layer)
The precursor solution is applied on a silicon oxide film of a negative electrode for a lithium ion secondary battery composed of a laminate of a copper thin film and a silicon oxide film, cured at room temperature (20 ° C.) for 60 hours, and mesoporous on the silicon oxide film. A layer (thickness: 5 μm) was formed. When the internal structure was observed by SEM, it was confirmed that the pore diameter was 500 nm on average and a continuous pore structure having a porosity of 70% was formed.

(Manufacture of lithium ion secondary batteries)
A commercially available ternary positive electrode (manufactured by PIOTREK) and a negative electrode for a lithium ion secondary battery having a mesoporous layer formed thereon were punched into disks each having a diameter of 16 mm.

The obtained positive electrode and the negative electrode for a lithium ion secondary battery on which a mesoporous layer is formed are laminated in this order in a SUS battery container (CR2032), and an electrolytic solution comprising EC / DEC (3: 7 vol%) and 1M LiPF _{6 is formed.} The liquid was impregnated into a positive electrode and a negative electrode for a lithium ion secondary battery on which a mesoporous layer was formed. Further, a SUS plate (thickness: 1.2 mm, diameter: 16 mm) was placed on the negative electrode, and a lid was manufactured, thereby manufacturing a lithium ion secondary battery as a coin-type cell.

(Comparative example)
A commercially available ternary positive electrode (manufactured by PIOTREK) and a negative electrode for a lithium ion secondary battery formed by laminating a copper thin film and a SiOx film were punched into disks each having a diameter of 16 mm. Further, a separator made of glass fiber was used, and was punched into a disk having a diameter of 17 mm.

The obtained positive electrode, separator, and negative electrode were laminated in this order in a battery container (CR2032) made of SUS, and an electrolytic solution composed of EC / DEC (3: 7 vol%) and 1M LiPF ₆ was charged with the positive electrode, the separator, and the negative electrode. Was impregnated. Further, a SUS plate (thickness: 1.2 mm, diameter: 16 mm) was placed on the negative electrode, and a lid was manufactured, thereby manufacturing a lithium ion secondary battery as a coin-type cell.

  The coin-type lithium ion secondary batteries produced in Example 1 and Comparative Example were stored at 25 ° C. for 5 hours, charged and discharged at 0.2 C, and then left at −10 ° C. for 5 hours. Thereafter, the battery was charged at -10 ° C. at 1 C, and the coin-type lithium ion secondary battery was disassembled. As a result, no lithium deposition was observed on the negative electrode of the coin-type lithium ion secondary battery manufactured in Example 1, but lithium was deposited on the negative electrode of the coin-type lithium ion secondary battery manufactured in the comparative example. Was observed.

  DESCRIPTION OF SYMBOLS 1 ... electrode, 1a ... collector, 1b ... electrode active material layer, 1c ... mesoporous layer, 2 ... electrolyte, 10 ... lithium ion secondary battery, 11 ... negative electrode, 12 ... positive electrode, 11a ... collector, 11b ... Negative electrode active material layer, 11c: mesoporous layer, 12a: current collector, 12b: positive electrode active material layer.

Claims (8)

A current collector, an electrode active material layer, and an insulating mesoporous layer are arranged in this order ,
An electrode for a lithium ion secondary battery , wherein the mesoporous layer includes a structure represented by the formula (1) .
[Formula 1]

(In the formula (1), X is an —O— bond or an OH group, R ¹ is a hydrocarbon group having 1 to 50 carbon atoms, and R ² is any one of a methyl, ethyl, propyl, and phenyl group. Represents a group, and n1 and n2 are either 0, 1 or 2, and at least one of n1 and n2 is 1 or 2.)   The electrode for a lithium ion secondary battery according to claim 1, wherein the electrode for a lithium ion secondary battery is a negative electrode, and a covalent bond is formed in at least a part of an interface between the electrode active material layer and the mesoporous layer. .   The electrode for a lithium ion secondary battery according to claim 1, wherein the electrode for a lithium ion secondary battery is a positive electrode, and a covalent bond is formed at least at a part of an interface between the electrode active material layer and the mesoporous layer. .   The electrode for a lithium ion secondary battery according to claim 2, wherein the electrode active material layer contains silicon or silicon oxide.   The electrode for a lithium ion secondary battery according to claim 3, wherein the electrode active material layer includes a metal oxide.   A lithium ion secondary battery provided with the electrode for a lithium ion secondary battery according to claim 1. A step of applying a precursor solution containing an organic-inorganic composite crosslinking compound having a crosslinkable silyl group and a carbon atom covalently bonded thereto to the surface of the electrode active material layer laminated on the current collector,
Hydrolyzing and condensing the crosslinkable silyl group of the organic-inorganic composite crosslinkable compound in the precursor solution to form an insulating mesoporous layer on the surface of the electrode active material layer. A method for producing an electrode for a lithium ion secondary battery comprising: A step of applying a precursor solution containing an organic-inorganic composite crosslinkable compound having a crosslinkable silyl group and a carbon atom covalently bonded thereto to a substrate,
A step of forming an insulating mesoporous layer on the substrate by hydrolyzing and condensing the crosslinkable silyl group,
Separating the insulating mesoporous layer from the substrate;
A primer solution containing a silane coupling agent is applied to one surface of the mesoporous layer, and the applied surface is brought into contact with the surface of the electrode active material layer laminated on the current collector, whereby the electrode active material layer Adhering the insulating mesoporous layer to the surface via the silane coupling agent, and a method for producing an electrode for a lithium ion secondary battery.

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